This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. xc2xa7119 from an application for ATM SWITCHING DEVICE AND METHOD CAPABLE OF PROVIDING VOICE CALL SERVICE earlier filed in the Korean Industrial Property Office on Jun. 11, 1997, and there duly assigned Serial No. 24032/1997, a copy of which application is annexed hereto.
1. Technical Field
The present invention relates to asynchronous transfer mode (ATM) switching device, and in particular, relates to an ATM switching device and method capable of providing voice call service.
2. Related Art
Generally, ATM is a specific packet-oriented transfer mode using an asynchronous time division multiplexing technique where both circuit switching and packet switching are unified and many pieces of data information such as voice, video, and data are organized in fixed-sized blocks, called cells. ATM can operate as both a packet exchange system and a circuit exchange system in one transmission mode for efficiently embodying both high speed and wide band communication networks. For this reason, ATM is a target transfer mode solution for implementing a broadband integrated services digital network (B-ISDN) because it offers an effective information channel management, and serves to decrease the costs of broad-band communication network facilities because of its flexibility in a bandwidth distribution.
ATM technology has since been implemented for broadband-integrated service digital networks (B-ISDN) to provide service for a wide variety of applications such as voice, video, and data. Each of these applications has different service requirements in terms of cell loss and cell delay. For example, voice traffic can withstand a small amount of cell loss, but it is intolerant to cell delay. Video traffic can typically tolerate a small amount of cell loss, but it is sensitive to cell delay. Data traffic can withstand a considerable amount of cell delay, but it is intolerant to cell loss. Voice service for ATM network remains a challenge because an ATM switch relies on a different voice data transmission from that of a currently used circuit switch. Therefore, an additional function for accommodating voice data must be provided to the ATM switch during its transition period. Recent studies have been conducted to provide voice service for subscribers connected to a public switched telephone network (PSTN) through interworking functions between the PSTN and an ATM network. However, cell delay and the decrease of bandwidth efficiency involved in assembling voice data output from the PSTN into an ATM cell still remain problems.
There have been some proposals of an ATM network using both a STM (i.e., Synchronous Transfer Mode) switch which is ideal for voice service and an ATM switch to simultaneously provide general circuit switching and ATM switching. Some examples of these ATM networks are disclosed in U.S. Pat. No. 5,173,901 for Communication System For Transmitting Synchronous And Asynchronous Cell Streams Over A Single Transmission Link issued to DeSomer, U.S. Pat. No. 5,204,857 for ATM Exchange System issued to Obera, U.S. Pat. No. 5,301,189 for Telecommunication Network Having ATM Switching Centers And STM Switching Centers issued to Schmidt et al., U.S. Pat. No.5,483,527 for Terminal Adapter For Interfacing An ATM Network With A STM Network issued to Doshi et al., U.S. Pat. No. 5,568,475 for ATM Network Architecture Employing An Out-Of-Band Signal Network issued to Doshi. Generally, such ATM networks are designed to concurrently provide STM and ATM with common hardware and software platform, and accommodate any of an STM node, an ATM node, and an STM/ATM composite node. However, I have observed that there are a number of drawbacks. For example, both STM and ATM switches are required to implement STM and ATM switchings independently. Traffic control is complex and a large traffic load between the STM and ATM switches may cause a bottle-neck. Cells are typically delayed, and the delay in assembling voice data into a cell has an adverse influence on voice quality. Lastly, cell bandwidth efficiency is decreased.
Other proposals to minimize the drawbacks of typical ATM networks are disclosed, for example, in U.S. Pat. No. 5,144,619 for Common Memory Switch For Routing Data Signals Comprising ATM And STM Cells issued to Munter, U.S. Pat. No. 5,168,492 for Rotating-Access ATM-STM Packet Switch issued to Beshai et al., U.S. Pat. No. 5,359,600 for High Throughput Supervisory System For ATM Switching Systems Transporting STM-N Signals issued to Ueda et al., and U.S. Pat. No. 5,390,184 for Flexible Scheduling Mechanism For ATM Switches issued to Morris, and U.S. Pat. No. 5,577,037 for Method Of Processing Inclusively STM Signals And ATM Signals And Switching System Employing The Same issued to Takatori et al. For example, Munter ""619 proposes the use of a single ATM switch for handling both ATM and STM traffic. An STM signal is first packetized, which may be time consuming, and is then processed in the similar manner to an ATM signal. A switching unit operates to switch both the STM signal, which has been packetized, and the ATM signal in accordance with the information that has been written to the respective headers. Morris ""184 discloses a flexible scheduling mechanism in an ATM switch for use in lieu of a separate STM switch for handling ATM and STM traffic. Takatori ""037 seeks to separately manage both ATM and STM signals to minimize the time delay in packetizing the STM signal for exchange in a single ATM system. While the contemporary proposals for ATM networks to handle both ATM and STM traffic with a single switch contain their own merits, I believe that further improvements for ATM networks to effectively provide general voice service from the PSTN are still necessary.
Accordingly, it is therefore an object of the present invention to provide an ATM switching device which can concurrently handle both ATM and STM traffic with a single switch.
It is also an object to provide an ATM switching device which can complete routing of both ATM and STM traffic in a single switch.
It is further an object to provide an ATM switching device which can prevent cell transmission delay by assembling voice data of different channels into a cell every frame period.
It is yet another object to provide an ATM switching device which can concurrently process both ATM and STM traffic, and remove a bottle-neck at interworking functions for interworking functioning between STM traffic and ATM traffic by scattering the interworking functions at respective ports of a switch.
These and other objects of the present invention can be achieved by an ATM switching device for providing voice call service. The ATM switching device comprises an input time switch module connected to an input PSTN interface for switching DS0 channel data received over sub-highways to voice stream data grouped in accordance with destinations by sorting the received DS0 channel data according to time slots corresponding to numbers of destination time switch modules. An input cell assembly and disassembly module assembles a group of voice data headed for the same destination into an identical ATM upon receipt from the input time switch module. An ATM switch is connected to the input cell assembly and disassembly module and an ATM interface for self-routing the ATM cell received from the input cell assembly and disassembly module, switching the ATM cell, and outputting the switched ATM cell to a corresponding destination. A destination cell assembly and disassembly module disassembles the ATM cell received from the ATM switch into voice stream data. An output time switch module is connected between the destination cell assembly and disassembly module and a destination PSTN interface for interchanging time slots of the disassembled voice stream data according to destinations, and outputting each of the time-slot interchanged voice stream data to a corresponding PSTN destination interface.
The present invention is more specifically described in the following paragraphs by reference to the drawings attached only by way of example.